The present invention relates to municipal castings and more particularly to municipal casting frames that support covers, and to method for manufacturing the same.
Municipal castings are a broad range of products used in conjunction with municipal and construction applications to enclose, trim and/or provide access to infrastructure, such as drainage and sewer infrastructure. Some of the most common municipal castings include manholes, covers and frames.
In many applications, municipal casting are used in connection with an access point to underlying infrastructure. For example, municipal casting may be used to provide a frame and cover over an access point to the infrastructure. Typically, the frame will be securely affixed to the infrastructure in an essentially permanent manner. The cover will be removably fitted to the frame to close the access opening.
If desired, a cover and frame may be configured to allow the cover to be bolted to the frame. This provides improved security and helps to avoid unauthorized and inadvertent removal of the cover from the frame. In conventional applications where a bolt-down cover is desired, a specially configured frame is installed. The frame is typically provided with lugs that are drilled and tapped to provide structure for threadedly receiving a bolt. The process of a preparing a frame for use in a bolt-down application adds additional cost. Accordingly, it is desirable to prepare a frame for bolts only when a bolt-down cover is expected. As a result, the majority of existing and new frame installations do not include a frame that is configured for a bolt-down cover.
It is not uncommon for a customer to request conversion of an installation from a standard cover to a bolt-down cover. If the installation includes a frame prepared for a bolt-down cover, the conversion process is simple and straightforward. However, if the installation does not include such a frame, it is necessary to either replace the frame or perform field modifications to the frame. Typical field modifications include drilling and tapping holes in the frame capable of receiving the cover bolts. In some applications, the frame may not be suitable for field modifications of this type. For example, the frame may not include a wide enough support flange to be drilled and tapped for this purpose. Further, with repeated use, threads can be damaged. If the threads become damaged, it may be necessary to replace the frame or to undergo even more extensive field modifications.
In an effort to facilitate the use of bolt-down covers, some existing frames include one or more nut shelves on the undersurface of the frame in alignment with the bolt holes. The nut shelves include a plurality of walls that define a nut compartment beneath each bolt hole. In use, a nut is slid sideways into the nut compartment. The nut shelf loosely holds the nut beneath the bolt hole and prevents it from rotating when a bolt is installed. Although an improvement in some respects, experience has revealed that it can be difficult to align the nut with the bolt hole and that the nut can move within the slot making it difficult to install the bolts.